Dielectric layers and memory cells including metal-doped alumina

ABSTRACT

A method of forming (and an apparatus for forming) a metal-doped aluminum oxide layer on a substrate, particularly a semiconductor substrate or substrate assembly, using a vapor deposition process.

RELATED PATENT DATA

This patent resulted from a divisional application of U.S. patentapplication Ser. No. 12/725,753, filed Mar. 17, 2010, entitled“Dielectric Layers and Memory Cells Including Metal-Doped Alumina”,naming Brian A. Vaartstra as inventor, which resulted from a divisionalapplication of U.S. patent application Ser. No. 12/345,245, filed Dec.29, 2008, now U.S. Pat. No. 7,683,001, entitled “Dielectric Layers andMemory Cells Including Metal-Doped Alumina”, naming Brian A. Vaartstraas inventor, which resulted from a divisional application of U.S. patentapplication Ser. No. 11/131,165, filed May 17, 2005, now U.S. Pat. No.7,473,662, entitled “Dielectric Layers and Memory Cells IncludingMetal-Doped Alumina”, naming Brian A. Vaartstra as inventor, whichresulted from a divisional application of U.S. patent application Ser.No. 10/229,780, filed Aug. 28, 2002, now U.S. Pat. No. 6,984,592,entitled “Dielectric Layers and Memory Cells Including Metal-DopedAlumina”, naming Brian A. Vaartstra as inventor, the disclosures ofwhich are incorporated by reference.

FIELD OF THE INVENTION

This invention relates to methods of forming a metal-doped aluminumoxide layer on a substrate using one or more lanthanide precursorcompounds that include one or more diketonate ligands and/or ketoimineligands and/or organo-oxide ligands during a vapor deposition process.The precursor compounds and methods are particularly suitable for theformation of metal-doped aluminum oxide layers on semiconductorsubstrates or substrate assemblies.

BACKGROUND OF THE INVENTION

The continuous shrinkage of microelectronic devices such as capacitorsand gates over the years has led to a situation where the materialstraditionally used in integrated circuit technology are approachingtheir performance limits. Silicon (i.e., doped polysilicon) hasgenerally been the substrate of choice, and silicon dioxide (SiO₂) hasfrequently been used as the dielectric material with silicon toconstruct microelectronic devices. However, when the SiO₂ layer isthinned to 1 nm (i.e., a thickness of only 4 or 5 molecules), as isdesired in the newest micro devices, the layer no longer effectivelyperforms as an insulator due to the tunneling current running throughit.

Thus, new high dielectric constant materials are needed to extend deviceperformance. Such materials need to demonstrate high permittivity,barrier height to prevent tunneling, stability in direct contact withsilicon, and good interface quality and film morphology. Furthermore,such materials must be compatible with the gate material, electrodes,semiconductor processing temperatures, and operating conditions.

High quality thin oxide films of metals, such as ZrO₂, HfO₂, Al₂O₃, andYSZ deposited on semiconductor wafers have recently gained interest foruse in memories (e.g., dynamic random access memory (DRAM) devices,static random access memory (SRAM) devices, and ferroelectric memory(FERAM) devices). These materials have high dielectric constants andtherefore are attractive as replacements in memories for SiO₂ where verythin layers are required. These metal oxide layers are thermodynamicallystable in the presence of silicon, minimizing silicon oxidation uponthermal annealing, and appear to be compatible with metal gateelectrodes. Specifically, alumina (Al₂O₃) is very stable on silicon butits dielectric constant is only marginally better than silicon oxide andnitride. However, the addition of other metal oxides to the alumina canenhance the dielectric constant and extend the usefulness of thematerial to the next generation devices.

This discovery has led to an effort to investigate various depositionprocesses to form layers, especially dielectric layers, based on metaloxides. Such deposition processes have included vapor deposition, metalthermal oxidation, and high vacuum sputtering. Vapor depositionprocesses, which includes chemical vapor deposition (CVD) and atomiclayer deposition (ALD), are very appealing as they provide for excellentcontrol of dielectric uniformity and thickness on a substrate. But vapordeposition processes typically involve the co-reaction of reactive metalprecursor compounds with an oxygen source such as oxygen or water,either of which can cause formation of an undesirable SiO₂ interfaciallayer. Thus, an effort is underway to develop water- and oxygen-freevapor deposition processes for metal dopes alumina deposition.

Despite continual improvements in the deposition of semiconductordielectric layers, there remains a need for materials with highdielectric constants that are readily integrated with semiconductorprocesses using a vapor deposition process.

SUMMARY OF THE INVENTION

This invention provides methods of forming a metal-doped aluminum oxide(i.e., alumina) layer on a substrate, particularly a semiconductorsubstrate or substrate assembly, using a vapor deposition technique. Themethods involve forming the layer by combining one or more yttrium orlanthanide diketonate and/or ketoimine and/or organo-oxide precursorcompounds with one or more aluminum precursor compounds. The latteraluminum precursor compounds, for example, are typically metal alkyls,metal organo amines, or combinations thereof. Significantly, the methodsof the present invention do not require the use of water or a strongoxidizer, thus reducing (and typically avoiding) the problem ofproducing an undesirable interfacial oxide layer between the desiredmeal-containing layer and the substrate.

The methods of the present invention involve forming a metal-dopedaluminum oxide layer on a substrate by reacting one or more precursorcompounds the formula M(keto)_(y) (Formula I) with one or more aluminumprecursor compounds of the formula AlY₃ (Formula II). In Formulas I andII: M is a yttrium, scandium, or a lanthanide (La, Ce, Pr, Nd, etc.);each “keto” is independently a diketonate or ketoimine ligand; each Ygroup is independently R¹ or an amine of the formula (NR²R³), whereineach R¹, R², and R³ is independently hydrogen or an organic group; and yis 0 to 5 and is dependent on the oxidation state of M.

In one embodiment, the present invention provides a method of forming ametal-doped aluminum oxide layer on a substrate (e.g., as in a processof manufacturing a semiconductor structure). The method includes:providing a substrate (e.g., semiconductor substrate or substrateassembly); providing at least one precursor compound of the formulaM(keto)_(y) (Formula I) and at least one precursor compound of theformula AlY₃ (Formula II) as defined above; and contacting the precursorcompounds to form a metal-doped aluminum oxide layer on the substrate(e.g., one or more surfaces of the semiconductor substrate or substrateassembly) using a vapor deposition process.

In another embodiment, the present invention provides a method offorming a metal-doped aluminum oxide layer on a substrate (e.g., as in aprocess of manufacturing a semiconductor structure). The methodincludes: providing a substrate (e.g., a semiconductor substrate orsubstrate assembly) within a deposition chamber; providing at least oneprecursor compound of the formula M(keto)_(y) (Formula I) and at leastone precursor compound of the formula AlY₃ (Formula II) as definedabove; and vaporizing the precursor compounds to form vaporizedprecursor compounds; and directing the vaporized precursor compounds tothe substrate to form a metal-doped aluminum oxide layer (e.g.,dielectric layer) on one or more surfaces of the substrate.

In yet another embodiment, the present invention provides a method ofmanufacturing a memory device structure (e.g., a capacitor). The methodincludes: providing a substrate having a first electrode thereon;providing at least one precursor compound of the formula M(keto)_(y)(Formula I) and at least one precursor compound of the formula AlY₃(Formula II) as defined above; and vaporizing the precursor compounds toform vaporized precursor compounds; directing the vaporized precursorcompounds to the substrate to form a metal oxide dielectric layer on thefirst electrode of the substrate; and forming a second electrode on thedielectric layer.

The methods of the present invention can utilize a chemical vapordeposition (CVD) process, which can be pulsed, or an atomic layerdeposition (ALD) process (a self-limiting vapor deposition process thatincludes a plurality of deposition cycles, typically with purgingbetween the cycles). Preferably, the methods of the present inventionuse ALD. For certain ALD processes, the precursor compounds can bealternately introduced into a deposition chamber during each depositioncycle.

The present invention also provides a vapor deposition apparatus thatincludes: a vapor deposition chamber having a substrate positionedtherein; one or more vessels comprising one or more precursor compoundshaving the formula M(keto)_(y) (Formula I); and one or more vesselscomprising one or more one precursor compounds of the formula AlY₃(Formula II).

The present invention also provides a metal-doped aluminum oxide, whichis preferably in the form of a dielectric layer. The present inventionalso provides a memory cell (preferably a capacitor) that includes analuminum oxide layer doped with yttrium, scandium, or a lanthanide.Preferably, the ratio of yttrium, scandium, or a lanthanide to aluminumis less than 3:5. More preferably, the ratio of yttrium, scandium, or alanthanide to aluminum is about 1:99 to about 6:94. Preferably, themetal-doped aluminum oxide layer is amorphous.

“Semiconductor substrate” or “substrate assembly” as used herein refersto a semiconductor substrate such as a base semiconductor layer or asemiconductor substrate having one or more layers, structures, orregions formed thereon. A base semiconductor layer is typically thelowest layer of silicon material on a wafer or a silicon layer depositedon another material, such as silicon on sapphire. When reference is madeto a substrate assembly, various process steps may have been previouslyused to form or define regions, junctions, various structures orfeatures, and openings such as capacitor plates or barriers forcapacitors.

“Layer” as used herein refers to any metal-containing layer that can beformed on a substrate from the precursor compounds of this inventionusing a vapor deposition process. The term “layer” is meant to includelayers specific to the semiconductor industry, such as “barrier layer,”“dielectric layer,” and “conductive layer.” (The term “layer” issynonymous with the term “film” frequently used in the semiconductorindustry.) The term “layer” is also meant to include layers found intechnology outside of semiconductor technology, such as coatings onglass.

“Precursor compound” as used herein refers to a metal diketonate, metalketoimine compound, metal halide, metal organo-amine, metal alkyl, forexample, capable of forming, either alone or with other precursorcompounds, a metal-doped aluminum oxide layer on a substrate in a vapordeposition process.

“Deposition process” and “vapor deposition process” as used herein referto a process in which a metal-containing layer is formed on one or moresurfaces of a substrate (e.g., a doped polysilicon wafer) from vaporizedprecursor compound(s). Specifically, one or more metal precursorcompounds are vaporized and directed to one or more surfaces of a heatedsubstrate (e.g., semiconductor substrate or substrate assembly) placedin a deposition chamber. These precursor compounds form (e.g., byreacting or decomposing) a non-volatile, thin, uniform, metal-containinglayer on the surface(s) of the substrate. For the purposes of thisinvention, the term “vapor deposition process” is meant to include bothchemical vapor deposition processes (including pulsed chemical vapordeposition processes) and atomic layer deposition processes.

“Chemical vapor deposition” (CVD) as used herein refers to a vapordeposition process wherein the desired layer is deposited on thesubstrate from vaporized metal precursor compounds (and any reactiongases used) within a deposition chamber with no effort made to separatethe reaction components. In contrast to a “simple” CVD process thatinvolves the substantial simultaneous use of the precursor compounds andany reaction gases, “pulsed” CVD alternately pulses these materials intothe deposition chamber, but does not rigorously avoid intermixing of theprecursor and reaction gas streams, as is typically done in atomic layerdeposition or ALD (discussed in greater detail below).

“Atomic layer deposition” (ALD) as used herein refers to a vapordeposition process in which numerous consecutive deposition cycles areconducted in a deposition chamber. Typically, during each cycle themetal precursor is chemisorbed to the substrate surface; excessprecursor is purged out; a subsequent precursor and/or reaction gas isintroduced to react with the chemisorbed layer; and excess reaction gas(if used) and by-products are removed. As compared to the one cyclechemical vapor deposition (CVD) process, the longer duration multi-cycleALD process allows for improved control of layer thickness byself-limiting layer growth and minimizing detrimental gas phasereactions by separation of the reaction components. The term “atomiclayer deposition” as used herein is also meant to include the relatedterms “atomic layer epitaxy” (ALE), molecular beam epitaxy (MBE), gassource MBE, organometallic MBE, and chemical beam epitaxy when performedwith alternating pulses of precursor compound(s), reaction gas(es), andpurge (i.e., inert carrier) gas.

“Chemisorption” as used herein refers to the chemical adsorption ofvaporized reactive precursor compounds on the surface of a substrate.The adsorbed species are irreversibly bound to the substrate surface asa result of relatively strong binding forces characterized by highadsorption energies (e.g., >30 kcal/mol), comparable in strength toordinary chemical bonds. The chemisorbed species typically form amononolayer on the substrate surface. (See “The Condensed ChemicalDictionary”, 10th edition, revised by a G. G. Hawley, published by VanNostrand Reinhold Co., New York, 225 (1981)). The technique of ALD isbased on the principle of the formation of a saturated monolayer ofreactive precursor molecules by chemisorption. In ALD one or moreappropriate precursor compounds or reaction gases are alternatelyintroduced (e.g., pulsed) into a deposition chamber and chemisorbed ontothe surfaces of a substrate. Each sequential introduction of a reactivecompound (e.g., one or more precursor compounds and one or more reactiongases) is typically separated by an inert carrier gas purge. Eachprecursor compound co-reaction adds a new atomic layer to previouslydeposited layers to form a cumulative solid layer. The cycle isrepeated, typically for several hundred times, to gradually form thedesired layer thickness. It should be understood that ALD canalternately utilize one precursor compound, which is chemisorbed, andone reaction gas, which reacts with the chemisorbed species.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are exemplary capacitor constructions.

FIG. 4 is a perspective view of a vapor deposition coating systemsuitable for use in the method of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The present invention provides methods of forming a metal-doped aluminumoxide layer (i.e., a metal-doped alumina layer) on a substrate(preferably a semiconductor substrate or substrate assembly). Themethods of the present invention involve forming a metal-doped aluminumoxide layer on a substrate by combining one or more metal precursorcompounds the formula M(keto)_(y) (Formula I) with one or more metalprecursor compounds of the formula AlY₃ (Formula II). In Formulas I andII: M is yttrium, scandium, or a lanthanide (La, Ce, Pr, etc.); each“keto” is independently a diketonate or ketoimine ligand; each Y isindependently R¹ or an amine of the formula (NR²R³), wherein each R¹,R², and R³ is independently hydrogen or an organic group; and y is 0 to5 and is dependent on the oxidation state of M.

The metal-doped aluminum oxide layer typically includes less than a 3:5mole ratio of yttrium, scandium, or a lanthanide to aluminum).Preferably, it includes a range of ratios of about 0.01:99.99 to about10:90 of yttrium, scandium, or a lanthanide to aluminum. Morepreferably, it includes a range of ratios of about 1:99 to about 6:94 ofyttrium, scandium, or a lanthanide to aluminum. Preferably, themetal-doped aluminum oxide layer is amorphous. The metal-doped aluminumoxide layer is preferably a dielectric layer, which is preferably in amemory cell, such as a capacitor.

The substrate on which the metal-doped aluminum oxide layer is formed ispreferably a semiconductor substrate or substrate assembly. Any suitablesemiconductor material is contemplated, such as for example,conductively doped polysilicon (for this invention simply referred to as“silicon”). A substrate assembly may also contain a layer that includesplatinum, iridium, rhodium, ruthenium, ruthenium oxide, titaniumnitride, tantalum nitride, tantalum-silicon-nitride, silicon dioxide,aluminum, gallium arsenide, glass, etc., and other existing orto-be-developed materials used in semiconductor constructions, such asdynamic random access memory (DRAM) devices and static random accessmemory (SRAM) devices, for example.

Substrates other than semiconductor substrates or substrate assembliescan be used in methods of the present invention. These include, forexample, fibers, wires, etc. If the substrate is a semiconductorsubstrate or substrate assembly, the layers can be formed directly onthe lowest semiconductor surface of the substrate, or they can be formedon any of a variety of the layers (i.e., surfaces) as in a patternedwafer, for example.

The precursor compounds useful in this invention are of the formulasM(keto)_(y) (Formula I) and AlY₃ (Formula II). These compounds caninclude organic groups (as described in greater detail below).

As used herein, the term “organic group” is used for the purpose of thisinvention to mean a hydrocarbon group that is classified as an aliphaticgroup, cyclic group, or combination of aliphatic and cyclic groups(e.g., alkaryl and aralkyl groups). In the context of the presentinvention, suitable organic groups for precursor compounds of thisinvention are those that do not interfere with the formation of ametal-doped aluminum oxide layer using vapor deposition techniques. Inthe context of the present invention, the term “aliphatic group” means asaturated or unsaturated linear or branched hydrocarbon group. This termis used to encompass alkyl, alkenyl, and alkynyl groups, for example.The term “alkyl group” means a saturated linear or branched monovalenthydrocarbon group including, for example, methyl, ethyl, n-propyl,isopropyl, t-butyl, amyl, heptyl, and the like. The term “alkenyl group”means an unsaturated, linear or branched monovalent hydrocarbon groupwith one or more olefinically unsaturated groups (i.e., carbon-carbondouble bonds), such as a vinyl group. The term “alkynyl group” means anunsaturated, linear or branched monovalent hydrocarbon group with one ormore carbon-carbon triple bonds. The term “cyclic group” means a closedring hydrocarbon group that is classified as an alicyclic group,aromatic group, or heterocyclic group. The term “alicyclic group” meansa cyclic hydrocarbon group having properties resembling those ofaliphatic groups. The term “aromatic group” or “aryl group” means amono- or polynuclear aromatic hydrocarbon group. The term “heterocyclicgroup” means a closed ring hydrocarbon in which one or more of the atomsin the ring is an element other than carbon (e.g., nitrogen, oxygen,sulfur, etc.).

As a means of simplifying the discussion and the recitation of certainterminology used throughout this application, the terms “group” and“moiety” are used to differentiate between chemical species that allowfor substitution or that may be substituted and those that do not soallow for substitution or may not be so substituted. Thus, when the term“group” is used to describe a chemical substituent, the describedchemical material includes the unsubstituted group and that group withnonperoxidic O, N, S, Si, or F atoms, for example, in the chain as wellas carbonyl groups or other conventional substituents. Where the term“moiety” is used to describe a chemical compound or substituent, only anunsubstituted chemical material is intended to be included. For example,the phrase “alkyl group” is intended to include not only pure open chainsaturated hydrocarbon alkyl substituents, such as methyl, ethyl, propyl,1-butyl, and the like, but also alkyl substituents bearing furthersubstituents known in the art, such as hydroxy, alkoxy, alkylsulfonyl,halogen atoms, cyano, nitro, amino, carboxyl, etc. Thus, “alkyl group”includes ether groups, haloalkyls, nitroalkyls, carboxyalkyls,hydroxyalkyls, sulfoalkyls, etc. On the other hand, the phrase “alkylmoiety” is limited to the inclusion of only pure open chain saturatedhydrocarbon alkyl substituents, such as methyl, ethyl, propyl, t-butyl,and the like.

In Formula I: M is yttrium (Y), scandium (Sc), or a lanthanide (e.g.,La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, So, Er, Tm, Yb, Lu). For certainmethods of the present invention, preferably, M is selected from thegroup of Y, La, Ce, Pr, Gd, and mixtures thereof.

In Formula I, there can be up to 5 “keto” ligands (i.e., y=1-5).Typically, the number of “keto” ligands is dependent on the oxidationstate of M and on the value of n. Each “keto” ligand is independently adiketonate or ketoimine ligand. Preferably, there are 2-3 “keto” ligandsper metal (i.e., y=2-3). Preferably the “keto” ligand is of the formula(Formula IV):

wherein Z is O or NR⁷ and each R⁴, R⁵, R⁶, and R⁷ is independentlyhydrogen or an organic group. Preferably, each of the organic groupscontains 3-10 carbon atoms, more preferably, 1-6 carbon atoms, and mostpreferably, 1-4 carbon atoms. More preferably, the “keto” ligand is adiketonate wherein Z is O (oxygen).

In the “keto” ligands of Formula IV, more preferably, each R⁴, R⁵, R⁶,and R⁷ is independently H, or an organic group optionally containing oneor more heteroatoms (e.g., oxygen or nitrogen), fluorine atoms, orfunctional groups (e.g., a carbonyl group, a hydroxycarbyl group, or anaminocarbyl group). That is, included within the scope of Formula IV areligands wherein at least one R⁴, R⁵, R⁶, and R⁷ is an organic group andat least one carbon atom is replaced with one of a carbonyl group, ahydroxycarbyl group, an oxygen atom, a nitrogen atom, or an aminocarbylgroup. Also included within the scope of Formula IV are compoundswherein at least one R⁴, R⁵, R⁶, and R⁷ is an organic group and at leastone hydrogen atom in the organic group is replaced with a fluorine atom.Most preferably, the organic groups of Formula IV are (C1-C4)alkylgroups, which may be a linear, branched, or cyclic, as well as alkenylgroups (e.g., dienes and trienes), or alkynyl groups. In any of thesegroups, one or more of the hydrogen atoms can be replaced by fluorineatoms. Of these, the organic groups are preferably trifluoromethyl ortert-butyl. In one preferred embodiment, at least R⁵ is hydrogen. Morepreferably, R⁵ is hydrogen and R⁴ and R⁶ are tert-butyl. Morepreferably, R⁷ is methyl.

In Formula II, Y can be R¹ or an amine of the formula (NR²R³), whereineach of R¹, R², and R³ is independently hydrogen or an organic group.Preferably, each of the organic groups of R¹, R², and R³ contains 1-10carbon atoms, more preferably, 1-6 carbon atoms, and most preferably,1-4 carbon atoms. Preferably, at least one Y is R¹ wherein R¹ ishydrogen or an organic group, and more preferably, all the Y groups areR¹ wherein R¹ is an organic group.

In the Y groups of Formula II, each R¹, R², and R³ is independentlyhydrogen or an organic group optionally containing one or moreheteroatoms (e.g., oxygen or nitrogen), fluorine atoms, or functionalgroups (e.g., a carbonyl group, a hydroxycarbyl group, or an aminocarbylgroup). That is, included within the scope of the compounds of FormulaII are compounds wherein at least one R¹, R², and R³ is an organic groupwith at least one carbon atom in the organic group replaced with one ofa carbonyl group, a hydroxycarbyl group, an oxygen atom, a nitrogenatom, or an aminocarbyl group. Also included within the scope of thecompounds of Formula II are compounds wherein at least one R¹, R², andR³ is an organic group and at least one hydrogen atom in the organicgroup is replaced with a fluorine atom. Most preferably, the organicgroups of Formula II are (C1-C4)alkyl groups, which may be a linear orbranched groups, as well as alkenyl groups (e.g., dienes and trienes),or alkynyl groups. In any of these organic groups, one or more of thehydrogen atoms can be replaced by fluorine atoms. Of these, the organicgroups are preferably methyl moieties or cyclopentadienyl groups(substituted or unsubstituted). In one preferred embodiment, at leastone R¹, R², and R³ is methyl. More preferably, any R¹, R², and R³present is methyl (Me).

Examples of compounds of Formula I include La(thd)₃, Sc(thd)₃, Y(thd)₃,and Ce(thd)₃, wherein thd is tetramethylheptanedionate. Examples ofcompounds of Formula II include Al(CH₃)₃, Al(CH₂CH₃)₃, Al(N(CH₃)₂)₃, andAl(N(CH₃)₂)₂(NCH₂CH₂N(C₃)₂)₃.

The complexes of the present invention can be prepared by a variety ofmethods known to one of skill in the art. For example, complexes ofFormula I can be prepared by reaction of a metal hexamethyldisilazidewith appropriate equivalents of a dione such as2,2,6,6-tetramethyl-3,5-heptanedione. Complexes of Formula II wherein Yis an organic group can be prepared by reduction of the metal halides orreaction of the metal halides with Grignard reagents. Complexes ofFormula II wherein Y is an amine group can be prepared by reaction of ametal halide with lithium dialkylamide.

Various precursor compounds can be used in various combinations(typically, mixtures of compounds of Formula I or mixtures of compoundsof Formula II, but preferably no mixtures of compounds of Formulas I andII), optionally with one or more organic solvents (particularly for CVDprocesses), to form a precursor composition. The precursor compounds maybe liquids or solids at room temperature (preferably, they are liquidsat the vaporization temperature). Typically, they are liquidssufficiently volatile to be employed using known vapor depositiontechniques. However, as solids they may also be sufficiently volatilethat they can be vaporized or sublimed from the solid state using knownvapor deposition techniques. If they are less volatile solids, they arepreferably sufficiently soluble in an organic solvent or have meltingpoints below their decomposition temperatures such that they can be usedin flash vaporization, bubbling, microdroplet formation techniques, etc.Herein, vaporized precursor compounds may be used either alone oroptionally with vaporized molecules of other precursor compounds oroptionally with vaporized solvent molecules, if used As used herein,“liquid” refers to a solution or a neat liquid (a liquid at roomtemperature or a solid at room temperature that melts at an elevatedtemperature). As used herein, “solution” does not require completesolubility of the solid but may allow for some undissolved solid, aslong as there is a sufficient amount of the solid delivered by theorganic solvent into the vapor phase for chemical vapor depositionprocessing. If solvent dilution is used in deposition, the total molarconcentration of solvent vapor generated may also be considered as ainert carrier gas.

The solvents that are suitable for this application (particularly for aCVD process) can be one or more of the following: aliphatic hydrocarbonsor unsaturated hydrocarbons (C3-C20, and preferably C5-C10, cyclic,branched, or linear), aromatic hydrocarbons (C5-C20, and preferablyC5-C10), halogenated hydrocarbons, silylated hydrocarbons such asalkylsilanes, alkylsificates, ethers, polyethers, thioethers, esters,lactones, ammonia, amides, amines (aliphatic or aromatic, primary,secondary, or tertiary), polyamines, nitriles, cyanates, isocyanates,thiocyanates, silicone oils, alcohols, or compounds containingcombinations of any of the above or mixtures of one or more of theabove. The compounds are also generally compatible with each other, sothat mixtures of variable quantities of the precursor compounds will notinteract to significantly change their physical properties.

For this invention, preferably no reaction gas is employed to minimizeoxidation of the substrate (typically silicon) to its oxide (typicallysilicon dioxide). The “diketo”-containing precursor compound(s) providethe source of oxygen.

The precursor compounds can be vaporized in the presence of an inertcarrier gas if desired. Additionally, an inert carrier gas can be usedin purging steps in an ALD process. The inert carrier gas is typicallyselected from the group consisting of nitrogen, helium, argon, andcombinations thereof. In the context of the present invention, an inertcarrier gas is one that does not interfere with the formation of themetal-containing layer. Whether done in the presence of a inert carriergas or not, the vaporization is preferably done in the absence of oxygento avoid oxygen contamination of the layer (e.g., oxidation of siliconto form silicon dioxide).

The deposition process for this invention is a vapor deposition process.Vapor deposition processes are generally favored in the semiconductorindustry due to the process capability to quickly provide highlyconformal layers even within deep contacts and other openings. Chemicalvapor deposition (CVD) and atomic layer deposition (ALD) are two vapordeposition processes often employed to form thin, continuous, uniform,metal-containing (preferably dielectric) layers onto semiconductorsubstrates. Using either vapor deposition process, typically one or moreprecursor compounds are vaporized in a deposition chamber and optionallycombined with one or more reaction gases to form a metal-containinglayer onto a substrate. It will be readily apparent to one skilled inthe art that the vapor deposition process may be enhanced by employingvarious related techniques such as plasma assistance, photo assistance,laser assistance, as well as other techniques.

The final layer (preferably, a dielectric layer) formed preferably has athickness in the range of about 10 Å to about 500 Å. More preferably,the thickness of the metal-containing layer is in the range of about 30Å to about 80 Å.

In most vapor deposition processes, the precursor compound(s) aretypically reacted with an oxidizing or reducing reaction gas (e.g.,water vapor, oxygen or ammonia) at elevated temperatures to form themetal-containing layer. However, in the practice of this invention, nosuch reaction gas is needed as the precursor compound(s) provide thesource of oxygen needed in the vapor deposition process. However,oxidizing gases, such as O₂, O₃, H₂O, and H₂O₂, can be used if desired.

Chemical vapor deposition (CVD) has been extensively used for thepreparation of metal-containing layers, such as dielectric layers, insemiconductor processing because of its ability to provide highlyconformal and high quality dielectric layers at relatively fastprocessing times. The desired precursor compounds are vaporized and thenintroduced into a deposition chamber containing a heated substrate withoptional reaction gases and/or inert carrier gases. In a typical CVDprocess, vaporized precursors are contacted with reaction gas(es) at thesubstrate surface to form a layer (e.g., dielectric layer). The singledeposition cycle is allowed to continue until the desired thickness ofthe layer is achieved.

Typical CVD processes generally employ precursor compounds invaporization chambers that are separated from the process chamberwherein the deposition surface or wafer is located. For example, liquidprecursor compounds are typically placed in bubblers and heated to atemperature at which they vaporize, and the vaporized liquid precursorcompound is then transported by an inert carrier gas passing over thebubbler or through the liquid precursor compound. The vapors are thenswept through a gas line to the deposition chamber for depositing alayer on substrate surface(s) therein. Many techniques have beendeveloped to precisely control this process. For example, the amount ofprecursor material transported to the deposition chamber can beprecisely controlled by the temperature of the reservoir containing theprecursor compound and by the flow of an inert carrier gas bubbledthrough or passed over the reservoir.

Preferred embodiments of the precursor compounds described herein areparticularly suitable for chemical vapor deposition (CVD). Thedeposition temperature at the substrate surface is preferably held at atemperature in a range of about 100° C. to about 600° C., morepreferably in the range of about 200° C. to about 500° C. The depositionchamber pressure is preferably maintained at a deposition pressure ofabout 0.1 torr to about 10 torr. The partial pressure of precursorcompounds in the inert carrier gas is preferably about 0.001 torr toabout 10 torr.

Several modifications of the CVD process and chambers are possible, forexample, using atmospheric pressure chemical vapor deposition, lowpressure chemical vapor deposition (LPCVD), plasma enhanced chemicalvapor deposition (PECVD), hot wall or cold wall reactors or any otherchemical vapor deposition technique. Furthermore, pulsed CVD can beused, which is similar to ALD (discussed in greater detail below) butdoes not rigorously avoid intermixing of precursor and reactant gasstreams. Also, for pulsed CVD, the deposition thickness is dependent onthe exposure time, as opposed to ALD, which is self-limiting (discussedin greater detail below).

A typical CVD process may be carried out in a chemical vapor depositionreactor, such as a deposition chamber available under the tradedesignation of 7000 from Genus, Inc. (Sunnyvale, Calif.), a depositionchamber available under the trade designation of 5000 from AppliedMaterials, inc. (Santa Clara, Calif.), or a deposition chamber availableunder the trade designation of Prism from Novelus, Inc. (San Jose,Calif.). However, any deposition chamber suitable for performing CVD maybe used.

Alternatively, and preferably, the vapor deposition process employed inthe methods of the present invention is a multi-cycle ALD process. Sucha process is advantageous (particularly over a CVD process) in that inprovides for optimum control of atomic-level thickness and uniformity tothe deposited layer (e.g., dielectric layer) and to expose the metalprecursor compounds to lower volatilization and reaction temperatures tominimize degradation. Typically, in an ALD process, each reactant ispulsed sequentially onto a suitable substrate, typically at depositiontemperatures of about 25° C. to about 400° C. (preferably about 150° C.to about 300° C.), which is generally lower than presently used in CVDprocesses. Under such conditions the film growth is typicallyself-limiting (i.e., when the reactive sites on a surface are used up inan ALD process, the deposition generally stops), insuring not onlyexcellent conformality but also good large area uniformity plus simpleand accurate thickness control. Due to alternate dosing of the precursorcompounds and/or reaction gases, detrimental vapor-phase reactions areinherently eliminated, in contrast to the CVD process that is carriedout by continuous coreaction of the precursors and/or reaction gases.(See Vehkamäki et al, “Growth of SrTiO₃ and BaTiO₃ Thin Films by AtomicLayer Deposition,” Electrochemical and Solid-State Letters,2(10):504-506 (1999)).

A typical ALD process includes exposing an initial substrate to a firstchemical species (e.g., a silicon precursor compound) to accomplishchemisorption of the species onto the substrate. Theoretically, thechemisorption forms a monolayer that is uniformly one atom or moleculethick on the entire exposed initial substrate. In other words, asaturated monolayer. Practically, chemisorption might not occur on allportions of the substrate. Nevertheless, such an imperfect monolayer isstill a monolayer in the context of the present invention. In manyapplications, merely a substantially saturated monolayer may besuitable. A substantially saturated monolayer is one that will stillyield a deposited layer exhibiting the quality and/or properties desiredfor such layer.

The first species is purged from over the substrate and a secondchemical species (e.g., a different precursor compound) is provided toreact with the first monolayer of the first species. The second speciesis then purged and the steps are repeated with exposure of the secondspecies monolayer to the first species. In some cases, the twomonolayers may be of the same species. As an option, the second speciescan react with the first species, but not chemisorb additional materialthereto. That is, the second species can cleave some portion of thechemisorbed first species, altering such monolayer without forminganother monolayer thereon. Also, a third species or more may besuccessively chemisorbed (or reacted) and purged just as described forthe first and second species. Optionally, the second species (or thirdor subsequent) can include at least one reaction gas if desired.

Purging may involve a variety of techniques including, but not limitedto, contacting the substrate and/or monolayer with a carrier gas and/orlowering pressure to below the deposition pressure to reduce theconcentration of a species contacting the substrate and/or chemisorbedspecies. Examples of carrier gases include N₂, Ar, He, etc. Purging mayinstead include contacting the substrate and/or monolayer with anysubstance that allows chemisorption by-products to desorb and reducesthe concentration of a contacting species preparatory to introducinganother species. The contacting species may be reduced to some suitableconcentration or partial pressure known to those skilled in the artbased on the specifications for the product of a particular depositionprocess.

ALD is often described as a self-limiting process, in that a finitenumber of sites exist on a substrate to which the first species may formchemical bonds. The second species might only bond to the first speciesand thus may also be self-limiting. Once all of the finite number ofsites on a substrate are bonded with a first species, the first specieswill often not bond to other of the first species already bonded withthe substrate. However, process conditions can be varied in ALD topromote such bonding and render ALD not self-limiting. Accordingly, ALDmay also encompass a species forming other than one monolayer at a timeby stacking of a species, forming a layer more than one atom or moleculethick.

The described method indicates the “substantial absence” of the secondprecursor (i.e., second species) during chemisorption of the firstprecursor since insignificant amounts of the second precursor might bepresent. According to the knowledge and the preferences of those withordinary skill in the art, a determination can be made as to thetolerable amount of second precursor and process conditions selected toachieve the substantial absence of the second precursor.

Thus, during the ALD process, numerous consecutive deposition cycles areconducted in the deposition chamber, each cycle depositing a very thinmetal-containing layer (usually less than one monolayer such that thegrowth rate on average is from about 0.2 to about 3.0 Angstroms percycle), until a layer of the desired thickness is built up on thesubstrate of interest. The layer deposition is accomplished byalternately introducing (i.e., by pulsing) precursor compound(s) intothe deposition chamber containing a semiconductor substrate,chemisorbing the precursor compound(s) as a monolayer onto the substratesurfaces, and then reacting the chemisorbed precursor compound(s) withthe other co-reactive precursor compound(s). The pulse duration ofprecursor compound(s) and inert carrier gas(es) is sufficient tosaturate the substrate surface. Typically, the pulse duration is fromabout 0.1 second to about 5 seconds, preferably from about 0.2 second toabout 3 seconds, and more preferably from about 2 seconds to about 3seconds.

In comparison to the predominantly thermally driven CVD, ALD ispredominantly chemically driven. Accordingly, ALD is often conducted atmuch lower temperatures than CVD. During the ALD process, the substratetemperature is maintained at a temperature sufficiently low to maintainintact bonds between the chemisorbed precursor compound(s) and theunderlying substrate surface and to prevent decomposition of theprecursor compound(s). The temperature is also sufficiently high toavoid condensation of the precursor compounds(s). Typically thesubstrate temperature is kept within the range of about 25° C. to about400° C. (preferably about 150° C. to about 300° C., and more preferablyabout 250° C. to about 300° C.), which is generally lower than presentlyused in CVD processes. Thus, the first species or precursor compound ischemisorbed at this temperature. Surface reaction of the second speciesor precursor compound can occur at substantially the same temperature aschemisorption of the first precursor or, less preferably, at asubstantially different temperature. Clearly, some small variation intemperature, as judged by those of ordinary skill, can occur but stillbe a substantially same temperature by providing a reaction ratestatistically the same as would occur at the temperature of the firstprecursor chemisorption. Chemisorption and subsequent reactions couldinstead occur at exactly the same temperature.

For a typical ALD process, the pressure inside the deposition chamber iskept at about 10⁻⁴ torr to about 1 torr, preferably about 10⁻⁴ torr toabout 0.1 torr Typically, the deposition chamber is purged with an inertcarrier gas after the vaporized precursor compound(s) have beenintroduced into the chamber and/or reacted for each cycle. The inertcarrier gas(es) can also be introduced with the vaporized precursorcompound(s) during each cycle.

The reactivity of a precursor compound can significantly influence theprocess parameters in ALD. Under typical CVD process conditions, ahighly reactive compound may react in the gas phase generatingparticulates, depositing prematurely on undesired surfaces, producingpoor films, and/or yielding poor step coverage or otherwise yieldingnon-uniform deposition. For at least such reason, a highly reactivecompound might be considered not suitable for CVD. However, somecompounds not suitable for CVD are superior ALD precursors. For example,if the first precursor is gas phase reactive with the second precursor,such a combination of compounds might not be suitable for CVD, althoughthey could be used in ALD. In the CVD context, concern might also existregarding sticking coefficients and surface mobility, as known to thoseskilled in the art, when using highly gas-phase reactive precursors,however, little or no such concern would exist in the ALD context.

After layer formation on the substrate, an annealing process can beoptionally performed in situ in the deposition chamber in a nitrogenatmosphere or oxidizing atmosphere. Preferably, the annealingtemperature is within the range of about 400° C. to about 1000° C.Particularly after ALD, the annealing temperature is more preferablyabout 400° C. to about 750° C., and most preferably about 600° C. toabout 700° C. The annealing operation is preferably performed for a timeperiod of about 0.5 minute to about 60 minutes and more preferably for atime period of about 1 minute to about 10 minutes. One skilled in theart will recognize that such temperatures and time periods may vary. Forexample, furnace anneals and rapid thermal annealing may be used, andfurther, such anneals may be performed in one or more annealing steps.Preferably, no annealing is necessary.

As stated above, the use of the complexes and methods of forming filmsof the present invention are beneficial for a wide variety of thin filmapplications in semiconductor structures, particularly those using highdielectric materials. For example, such applications include gatedielectrics and capacitors such as planar cells, trench cells (e.g.,double sidewall trench capacitors), stacked cells (e.g., crown, V-cell,delta cell, multi-fingered, or cylindrical container stackedcapacitors), as well as field effect transistor devices.

A specific example of where a dielectric layer is formed according tothe present invention is a capacitor construction. Exemplary capacitorconstructions are described with reference to FIGS. 1-3. Referring toFIG. 1, a semiconductor wafer fragment 10 includes a capacitorconstruction 25 formed by a method of the present invention. Waferfragment 10 includes a substrate 12 having a conductive diffusion area14 formed therein. Substrate 12 can include, for example,monocrystalline silicon. An insulating layer 16, typicallyborophosphosilicate glass (BPSG), is provided over substrate 12, with acontact opening 18 provided therein to diffusion area 14. A conductivematerial 20 fills contact opening 18, with material 20 and oxide layer18 having been planarized as shown. Material 20 might be any suitableconductive material, such as, for example, tungsten or conductivelydoped polysilicon. Capacitor construction 25 is provided atop layer 16and plug 20, and electrically connected to node 14 through plug 20.

Capacitor construction 25 includes a first capacitor electrode 26, whichhas been provided and patterned over node 20. Exemplary materialsinclude conductively doped polysilicon, Pt, Ir, Rh, Ru, RuO₂, IrO₂,RhO₂. A capacitor dielectric layer 28 is provided over first capacitorelectrode 26. The materials of the present invention can be used to formthe capacitor dielectric layer 28. Preferably, if first capacitorelectrode 26 includes polysilicon, a surface of the polysilicon iscleaned by an in situ HF dip prior to deposition of the dielectricmaterial. An exemplary thickness for layer 28 in accordance with 256 Mbintegration is 100 Angstroms.

A diffusion barrier layer 30 is provided over dielectric layer 28.Diffusion barrier layer 30 includes conductive materials such as TiN,TaN, metal silicide, or metal silicide-nitride, and can be provided byCVD, for example, using conditions well known to those of skill in theart. After formation of barrier layer 30, a second capacitor electrode32 is formed over barrier layer 30 to complete construction of capacitor25. Second capacitor electrode 32 can include constructions similar tothose discussed above regarding the first capacitor electrode 26, andcan accordingly include, for example, conductively doped polysilicon.Diffusion barrier layer 30 preferably prevents components (e.g., oxygen)from diffusing from dielectric material 28 into electrode 32. If, forexample, oxygen diffuses into a silicon-containing electrode 32, it canundesirably form SiO₂, which will significantly reduce the capacitanceof capacitor 25. Diffusion barrier layer 30 can also prevent diffusionof silicon from metal electrode 32 to dielectric layer 28.

FIG. 2 illustrates an alternative embodiment of a capacitorconstruction. Like numerals from FIG. 1 have been utilized whereappropriate, with differences indicated by the suffix “a”. Waferfragment 10 a includes a capacitor construction 25 a differing from theconstruction 25 of FIG. 2 in provision of a barrier layer 30 a betweenfirst electrode 26 and dielectric layer 28, rather than betweendielectric layer 28 and second capacitor electrode 32. Barrier layer 30a can include constructions identical to those discussed above withreference to FIG. 1.

FIG. 3 illustrates yet another alternative embodiment of a capacitorconstruction. Like numerals from FIG. 1 are utilized where appropriate,with differences being indicated by the suffix “b” or by differentnumerals. Wafer fragment 10 b includes a capacitor construction 25 bhaving the first and second capacitor plate 26 and 32, respectively, ofthe first described embodiment. However, wafer fragment 10 b differsfrom wafer fragment 10 of FIG. 2 in that wafer fragment 10 b includes asecond barrier layer 40 in addition to the barrier layer 30. Barrierlayer 40 is provided between first capacitor electrode 26 and dielectriclayer 28, whereas barrier layer 30 is between second capacitor electrode32 and dielectric layer 28. Barrier layer 40 can be formed by methodsidentical to those discussed above with reference to FIG. 1 forformation of the barrier layer 30.

In the embodiments of FIGS. 1-3, the barrier layers are shown anddescribed as being distinct layers separate from the capacitorelectrodes. It is to be understood, however, that the barrier layers caninclude conductive materials and can accordingly, in such embodiments,be understood to include at least a portion of the capacitor electrodes.In particular embodiments an entirety of a capacitor electrode caninclude conductive barrier layer materials.

A system that can be used to perform vapor deposition processes(chemical vapor deposition or atomic layer deposition) of the presentinvention is shown in FIG. 4. The system includes an enclosed vapordeposition chamber 110, in which a vacuum may be created using turbopump 112 and backing pump 114. One or more substrates 116 (e.g.,semiconductor substrates or substrate assemblies) are positioned inchamber 110. A constant nominal temperature is established for substrate116, which can vary depending on the process used. Substrate 116 may beheated, for example, by an electrical resistance heater 118 on whichsubstrate 116 is mounted. Other known methods of heating the substratemay also be utilized.

In this process, precursor compounds 160 (e.g., a refractory metalprecursor compound and an ether) are stored in vessels 162. Theprecursor compounds are JO vaporized and separately fed along lines 164and 166 to the deposition chamber 110 using, for example, an inertcarrier gas 168. A reaction gas 170 may be supplied along line 172 asneeded. Also, a purge gas 174, which is often the same as the inertcarrier gas 168, may be supplied along line 176 as needed. As shown, aseries of valves 180-185 are opened and closed as required.

The following examples are offered to further illustrate the variousspecific and preferred embodiments and techniques. It should beunderstood, however, that many variations and modifications may be madewhile remaining within the scope of the present invention, so the scopeof the invention is not intended to be limited by the examples. Unlessspecified otherwise, all percentages shown in the examples arepercentages by weight.

EXAMPLE Example 1 Atomic Layer Deposition of (Y,Al)₂O₃

The deposition of (Y,Al)₂O₃ was carried out using alternating pulses ofY(thd)₃ (available from Strem Chemical Co., Newburyport, Mass.) andAl(Et)₃ (available from Rohm & Haas, Danvers, Mass.) vapor in an ALDprocess. The precursors were held at 190° C. and 50° C., respectively.The substrate had a top layer of 1500 Angstroms of doped polysilicon andwas held at 300° C. during 400 cycles. The film formed was approximately400 Angstroms thick and remained amorphous (as determined by XRD) evenafter a 750° C. anneal in nitrogen for 1 minute. The ratio of Yttrium toAluminum was determined by XPS and further identified by ICPspectroscopy to have an approximate stoichiometry of Y_(0.1)Al_(1.9)O₃.TEM showed an amorphous (Y,Al)₂O₃ with no apparent SiO₂ at theinterface. Electrical measurements were performed on the material bysputtering platinum electrodes on top of the film through a hard mask.The dielectric constant was 34 at 1 kHz and leakage was 8×10⁻⁹ A/cm².

The complete disclosures of the patents, patent documents, andpublications cited herein are incorporated by reference in theirentirety as if each were individually incorporated. Variousmodifications and alterations to this invention will become apparent tothose skilled in the art without departing from the scope and spirit ofthis invention. It should be understood that this invention is notintended to be unduly limited by the illustrative embodiments andexamples set forth herein and that such examples and embodiments arepresented by way of example only with the scope of the inventionintended to be limited only by the claims set forth herein as follows.

What is claimed is:
 1. A memory cell incorporating a dielectriccomposition comprising aluminum oxide and a mixture ofnon-stoichiometric amounts of lanthanides and wherein the molar ratio ofall of the lanthanides in the mixture to aluminum is about 1:99 to about10:90.
 2. The memory cell of claim 1 comprising a capacitor.
 3. Thememory cell of claim 2 wherein the capacitor comprises a capacitordielectric region comprising said dielectric composition.
 4. The memorycell of claim 1 wherein the mixture is of at least two of La, Ce, Pr,and Gd.
 5. The memory cell of claim 1 wherein the lanthanide comprisesLa.
 6. The memory cell of claim 1 wherein the lanthanide comprises Ce.7. The memory cell of claim 1 wherein the lanthanide comprises Pr. 8.The memory cell of claim 1 wherein the lanthanide comprises Gd.
 9. Thememory cell of claim 1 wherein the molar ratio of all of the lanthanidesin the mixture to aluminum is about 1:99 to about 6:94.
 10. The memorycell of claim 1 wherein the aluminum oxide has a thickness from about 10Angstroms to about 500 Angstroms.
 11. The memory cell of claim 10wherein the aluminum oxide has a thickness from about 30 Angstroms toabout 80 Angstroms.
 12. The memory cell of claim 10 wherein the aluminumoxide has a thickness of about 100 Angstroms.
 13. A memory devicestructure comprising: a substrate comprising a first electrode thereon;an amorphous dielectric composition comprising aluminum oxide and amixture of non-stoichiometric amounts of lanthanides and which is overthe first electrode, wherein the molar ratio of all of the lanthanidesin the mixture to aluminum is about 1:99 to about 10:90; and a secondelectrode over the dielectric composition.
 14. The memory cell of claim13 wherein the molar ratio of all of the lanthanides in the mixture toaluminum is about 1:99 to about 6:94.
 15. The memory device of claim 13wherein at least one of the first and second electrodes is in directcontact with the dielectric composition.
 16. The memory device of claim13 wherein at least one of the first and second electrodes comprises aconductive barrier material.
 17. The memory device of claim 13 whereinthe aluminum oxide has a thickness from about 10 Angstroms to about 500Angstroms.
 18. The memory device of claim 17 wherein the aluminum oxidehas a thickness from about 30 Angstroms to about 80 Angstroms.
 19. Thememory device of claim 17 wherein the aluminum oxide has a thickness ofabout 100 Angstroms.